Barnes was born in Boston, Massachusetts. He entered the Army in 1965 and received basic training at Fort Pickett. He was dispatched to Vietnam as part of the 173rd Airborne Brigade on May 31, 1966. Serving in Company C of the 1st Battalion, 503rd Infantry, Barnes was assigned as a grenadier. On November 12, 1967, while patrolling in the Kontum province, Barnes' unit was attacked by a North Vietnamese battalion. During the battle, Barnes manned a machine gun that had lost its crew to enemy fire and was credited with nine enemy kills. While retrieving more ammunition, Barnes dived on top of a grenade that had landed among American wounded in order to use his body to protect them from the blast. The grenade exploded, killing Barnes.

PFC Barnes was posthumously awarded the Medal of Honor for his actions.

MOH CITATION:

For conspicuous gallantry and intrepidity in action at the risk of his life above and beyond the call of duty. Pfc. Barnes distinguished himself by exceptional heroism while engaged in combat against hostile forces. Pfc. Barnes was serving as a grenadier when his unit was attacked by a North Vietnamese force, estimated to be a battalion. Upon seeing the crew of a machine gun team killed, Pfc. Barnes, without hesitation, dashed through the bullet swept area, manned the machine gun, and killed 9 enemy soldiers as they assaulted his position. While pausing just long enough to retrieve more ammunition, Pfc. Barnes observed an enemy grenade thrown into the midst of some severely wounded personnel close to his position. Realizing that the grenade could further injure or kill the majority of the wounded personnel, he sacrificed his life by throwing himself directly onto the hand grenade as it exploded.